This project is aimed at using the SV40 large T antigen to elucidate the mechanism(s) of cellular senescence in WI-38 cells. We intend to use the ability of SV40 large T antigen to induce DNA synthesis in senescent WI- 38 cells to study 3 aspects of cellular senescence: 1) the expression of the PCNA gene; 2) the roles of B-myb, IGF-1 receptor; and 3) the immortalization of HDF by a ts mutuant of SV40 large T antigen.